The invention concerns a process for the rotary truing of planks and the like around their longitudinal axes by means of a plank guide channel through which the planks pass in the longitudinal direction, said channel having a twist around the longitudinal axis which is variable by adjusting the parts forming the plank guide channel.
In the case of a known straightening apparatus (DE-B-32 07 548), planks and in particular planks cut from the sides of a flattened tree trunk by a chipless cutting method are straightened, together with similar flat wood products such as plates with a curvature around a transverse axis, between rolls.
However, primarily the boards or the like (also designated plates) produced by the chipless method described frequently exhibit in addition to the abovementioned curvature a twist, i.e. they are twisted or turned around their longitudinal axis. This deformation in numerous applications prevents any automatic further processing of the boards. The twist increases with the angle of inclination of the board-cutting blades with respect to the longitudinal direction of the trunk.
A known process of the abovementioned generic type (DE-A-37 01 127) is used to straighten the boards produced. For the purpose, the boards pass through a board guide channel with a spiral distortion, i.e. a twist around its longitudinal axis. In this manner, the boards are given a continuous twist in the course of their passage in a direction opposite to their original twist. In the process, the boards are straightened so that they then have a permanent straight shape.
The individual parts forming the board guide channel, for example pairs of rolls, may be pivoted, so that a more or less intensive twist of the board guide channel may be set as a function of the straightening effect required. It is possible in this fashion to adapt the known process as needed. The adjustment of the board guide channel is carried out in accordance with empirical values primarily as a function of the twist present in the untreated boards. If the boards still have twists after passing through the board guide channel, the setting of the board guide channel is altered until a satisfactory result is obtained. These adjustment activities are very expensive, mainly because the initial state of the boards varies frequently and because the physical and chemical properties of the wood also have a significant effect.
It is further known (DE-A-36 23 235), to utilize the humidity of the wood to regulate a processing parameter in the chipless cutting of boards from a tree trunk. In this process the measured value of the humidity of the wood is used to vary the contact pressure of a pressure beam which applies pressure to the point at which the boards are cut. No straightening process is involved.